AFAIK, no boards officially support ddr500 speeds. That said, ddr 500 will work in a motherboard that supports ddr400, but at ddr400 speed(it downclocks). Also, if you overclock, you can make the memory run at it's full clock speed, if you clock it high enough.

An example of this would be on an amd64 cpu, if I overclocked the htt speed to 250mhz, the memory would be at ddr500 speed(if I didn't use a memory divider).

If you don't understand that last part(I know it may sound like greek, if you aren't into that), don't worry, you don't need to unless you want to overclock your cpu.